Press section
Also: press section, press nip
The part of the paper machine after forming where water is squeezed from the wet sheet by passing it through pressurized roll nips with felts.
The press section removes water mechanically, which is far cheaper than evaporating it in the dryer. A modern shoe press squeezes the sheet in a wide nip with pressures up to 1400 kN/m, reducing sheet moisture from about 80% after forming to 40 to 50% going into the dryer.
Pressing also consolidates the fiber network, increasing strength. Press felts carry the sheet through the nips and absorb expressed water. Mills measure press efficiency by the dryness at the end of the press section: every percentage point of dryness gained cuts dryer steam use.
Related
- Fourdrinier. The traditional single-wire paper machine design where stock drains through a moving mesh. Invented 1803, still dominant for many grades.
- Dryer section. The part of the paper machine where the sheet dries to final moisture by contact with steam-heated cylinders.